The present invention relates to an arrangement and a method for a drive unit of a motor vehicle. Particularly, the invention relates to an apparatus and method for control of engine torque in mechanical stepped gearboxes, wherein there is a connection between the engine and a mechanical stepped gearbox to transmit rotary motion and there are means and a method of operation for acting on the connection, so that substantially no torque is transmitted from the engine to the gearbox.
In motor vehicles it is desirable to be able to change gear in a stepped gearbox without having to use the vehicle""s clutch. This has been achieved, according to known technology, by the engine being controlled so that substantially no torque is transmitted from the engine to the gearbox during a gear change, i.e. while disengaging from one gear and engaging another.
Methods are known from SE 504 717 correspoding to U.S. Pat. 5,859,886 and 5,866,809 and SE 502 807 corresponding to U.S. Pat. No, 5,595,551 for controlling the torque delivered by an engine to a level such that substantially no torque is transmitted to the gearbox during gear disengagement. Such control of engine torque and speed can be achieved by adjusting the fuel supply to the engine.
A known practice from SE 502 154 is for gear engagement when changing up to be preceded by using an exhaust brake to reduce the engine speed to such a level that a synchronous speed is reached between the gearwheels which are intended to mesh with one another in the gearbox.
Controlling an engine by adjusting the amount of fuel supplied is complicated in that the fuel quantity injected is usually controlled by other conditions, some of which are intended to minimise fuel consumption. Nor is using an exhaust brake to reduce engine speed quickly an ideal practice, since it generates noise which may be disturbing.
Arranging an electric rotor machine on an output shaft of an engine is known in other contexts. These include the use of such a rotor machine as a starter motor for quickly getting the ordinary engine running. It may also be used for damping engine vibration particularly at low engine speeds, and for providing extra power during vehicle acceleration
The object of the present invention is to make gear changing in a mechanical stepped gearbox possible, without using the vehicle""s clutch, by controlling torque and speed delivered to the gearbox during gear changing more quickly, more precisely and more quietly, than by using the known technology mentioned in the introduction.
This object is achieved by an arrangement which is characterised in that it incorporates an electric rotor machine connected to a connecting device. With such an electric rotor machine it is possible quickly, quietly and precisely to adjust torque delivered by the engine and its speed via the connecting device so that substantially no torque is transmitted to the gearbox during a gear change.
According to a preferred embodiment of the invention, said means incorporates a control unit designed to control the electric rotor machine. Such a control unit may be designed to use knowledge of necessary information concerning the state of the vehicle at the time to control a control device so that the rotor machine is loaded with a relevant electric voltage with a view to correcting the torque and speed of said connecting device to a desired level. This may entail the control unit being connected to a device designed to detect the engine speed. Such a device may for example be a sensor which detects the speed of a flywheel on the engine""s output shaft.
The control unit may also be connected to a device designed to detect a parameter related to the seed of an output shaft of the gearbox. Such a device may be a sensor which detects for example, the speed of the output shaft of the gearbox, the speed of the vehicle""s propeller shaft or the speed of the driving wheels.
According to a preferred embodiment of the invention, the control unit is designed so that, before the disengagement of a gear in the gearbox, the control unit controls the electric rotor machine so that the latter corrects the torque delivered by the engine to such a level that substantially no torque is transmitted to the gearbox. This means that when a positive driving torque is transmitted via the gearwheels enmeshed at the time the control unit will provide the electric rotor machine with a corresponding amount of negative retarding torque.
If instead a negative torque prevails in the gearwheels enmeshed at the time, which may occur when the vehicle is travelling downhill, the electric rotor machine will provide a corresponding positive driving torque. The gearwheels concerned will therefore not be subject to any torque when the gear concerned is disengaged.
According to another preferred embodiment of the invention, the control unit is designed so that, before the engagement of a gear in the gearbox, the control unit controls the electric rotor machine so that the connecting device is brought to a speed which is in proportion to the speed of an output shaft of the gearbox, this proportion being determined by the gear concerned. The control unit may in this case use knowledge of the speed of, for example, an output shaft of the gearbox and the gear concerned to calculate the speed at which the connecting device must be when the gear concerned is engaged. This will result, when changing up, in the electric rotor machine retarding the speed of the connecting device to the calculated level, and, when changing up, in its accelerating the connecting device to the calculated speed. This means that the relevant gearwheels in the gearbox which are intended to mesh will have a synchronous speed at which the gear concerned can be engaged.
According to another preferred embodiment, the electric rotor machine includes a stator and a rotor, and the rotor is arranged in the connecting device. This means that the electric rotor machine can directly transmit a torque or adjust the speed of the connecting device. By way of alternative, the rotor machine may be connected via a transmission element to the connecting device, thereby making it possible to achieve a gear change between them.
According to another preferred embodiment of the invention, the electric rotor machine is designed to function when necessary as a motor and provide torque to the connecting device and to function when necessary as a generator and retard the connecting device.
Such a rotor machine does not necessarily have only to act upon the connecting device during a gear change. A rotor machine which functions both as motor and generator may be connected to an electrical energy storage device which delivers electrical energy to the motor machine when it functions as a motor and receives electrical energy from the rotor machine when it functions as a generator. The energy extracted by reducing the speed of the connecting device may therefore be stored in the energy storage device. This energy may subsequently be used when the connecting device has to be provided with torque and speed. Said electrical energy storage device may include one or more electric batteries or, in the case of short-duration energy storage, take the form of one or more capacitors.
The present invention also includes a method of a drive unit according to the arrangement described above. On the basis of a known practice of arranging an electric rotor machine on an engine output shaft in a vehicle, the method is characterised in that the electric rotor machine is controlled so that substantially no torque is transmitted from the connecting device to the gearbox during gear changing. Very precise control of the torque and speed of the electric rotor machine is thus possible, unlike the situation according to the known technology whereby the electric rotor machine is substantially used for supplying energy to the ordinary engine and storing braking energy. The electric rotor machine is preferably controlled, before the disengagement of a gear in the gearbox, so as to correct the torque delivered from the engine to such a level that substantially no torque is transmitted to the gearbox. It is also advantageous if the electric rotor machine, before the engagement of a gear in the gearbox, is controlled so that the connecting device is brought to a speed which is in proportion to the speed of an output shaft of the gearbox, this proportion being determined by the gear concerned. Using the electric rotor machine in the foregoing manner makes it possible quickly and with great precision to adjust the torque and speed of the engine so that the disengagement and engagement of the relevant gears can take place without being affected by torque in the gearwheels enmeshed at the time in the gearbox.